Like all restaurants at the Wynn and Encore hotels, Allegro is super vegan/vegetarian friendly. Vegheads have their pick of a number of entrees that suit their preferences rather than having to piece together a meal using appetizers and sides. This was one of the best discoveries of my Vegas trip. They really need to advertise this better!
The service and atmosphere at Allegro are top notch. Being just off the casino floor, this restaurant is more casual than some of the other choices in the hotel but I was honestly surprised that it wasn't super noisy. It's a great place to people-watch while you eat.
As for the food? Très Bien! I was super impressed to note that the same amount of care went into making their vegetarian food as it did to their omnivore fare. My friend and I were having trouble choosing and ended up sharing the butternut squash ravioli and the vegan pizza made with almond ricotta and spinach fondue. I'm still dreaming about how amazing the pizza was! Think someone could mail me a slice??